Hi there vaishnu,
You can start with just reseating the drive. Make sure that the cables and ports are not loose.
If the issue persists, the best thing you can do is to take the drive out and attach it to another system as a secondary drive. This way, you can either access it right away or use some kind of data recovery software.
After you recover your data, I would advise you to test the drive with some kind of a testing tool(brand specific or a third party one). The results will show you whether there is something wrong with the drive. If there is, there will be no point in re-installing OS on it.
Cheers,
D_Know_WD